Very shallow geothermal potential in urban areas: parameterization algorithm and mapping tool for thermal conductivity and thermal resistivity in Warsaw (Poland)

Abstract

The transition toward Smart City development relies on efficient integration of digital and geoscientific data to improve the sustainability of urban infrastructure. A key component of this process is the optimal utilization of subsurface thermal resources for clean energy systems, as well as the planning of underground infrastructure. This study presents a novel adaptation of the national Engineering-Geological Database of Poland (BDGI) for mapping the very shallow geothermal potential of urban areas. Using more than 35,000 boreholes from the Warsaw region, the database was processed to generate spatial models of thermal conductivity (λ) and thermal resistivity (ρ) at depths from 2 to 30 m below ground level. The shallow thermal conductivity maps so prepared are particularly relevant for the design of energy geostructures (e.g., geothermal piles, thermoactive foundations, energy tunnels) and horizontal ground heat exchangers. The data shown as thermal resistivity maps can also support the design and operation of urban transmission infrastructures such as district heating, electricity, and water networks. The case study area is characterized by loose sediments and soils (compressive strength Rc Ł600 kPa, according to ISO 14689), while solid rocks were not considered as they do not occur at such shallow depths. The resulting thermal maps provide new insights into the spatial variability of the urban subsurface and constitute a practical geospatial tool for energy and infrastructure planning in sustainable city development.